The newly created cpp file through UE Editor does not appear in the solution in Rider, for it to appear, you need to close the IDE and re-open the cpp file. Only after the specified procedure, the files appear in the solution.
It usally appear automatically but when it doesn’t I switch my Explorer tab to FileSystem instead of Solution to see if the file is here and then revert back to Solution

When this doesn’t work i refresh Rider from the editor

Work all the times
This approach does not work, I also assumed it before)
Worked for me, Thank you!
